The microstructural modifications occurring during annealing treatment of an Fe-0.35 C-3.5 Mn-5.8 Al ferrite-based lightweight steel and its effects on the tensile properties were investigated with respect to (α + γ) duplex microstructures. Steels annealed above the dissolution finishing temperature of κ-carbides (795 C) were basically composed of ferrite band and austenite band in a layered structure. As the annealing temperature was increased the tensile strength increased, while the yield strength and elongation decreased. This could be explained by a decrease in the mechanical as well as thermal stability of austenite with increasing size and austenite volume fraction. In the 980 C annealed steel in particular, whose mechanical stability due to austenite was lowest, cracks were readily formed at ferrite/austenite (or martensite) interfaces with little deformation, thereby leading to the least tensile elongation. In order to obtain the best combination of strength and ductility the formation of austenite having an appropriate mechanical stability was essentially needed, and could be achieved when 22-24 vol.% fine austenite was homogeneously distributed in the ferrite matrix, as in the 830 C or 880 C annealed steels.
Bibliographical noteFunding Information:
This work was supported by the Ministry of Knowledge Economy under a Grant No. 10031723-2011-21 . The authors would like to thank Mr Hyuk-Joong Lee of POSTECH, Dr Seung Youb Han of SK Innovation, and Dr Chang-hyo Seo of POSCO for their help with the alloying effects and microstructural analysis.
Copyright 2013 Elsevier B.V., All rights reserved.
- Duplex microstructure
- Lightweight steel
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys